1. Field of the Invention
This invention relates to rubber compositions for use in tires, which improve heat build-up by using carbon black with an improved higher order structure and are useful in the improvement of low rolling resistance of the tire.
2. Description of the Prior Art
The development of low fuel consumption tires has been promoted in correspondence with social demands directed to energy-saving. As a part of this development, a requirement exists to develop rubber compositions having good reinforcing properties and fatigue properties and an improved heat build-up.
As a countermeasure for such demand, it has been attempted to improve the heat build-up by making a half value width [.DELTA.D.sub.50 (st)] in aggregate distribution of carbon black large as disclosed in Japanese Patent laid open No. 56-106,936, which is mainly resulting in success as a rubber composition for tire tread.
Among rubber compositions suitable for use in portions other than the tire tread using low heat build-up carbon black, however, rubber compositions satisfying both fatigue properties and heat build-up are not still obtained at present.
That is, in these rubber compositions, when the structure of carbon black is made high, modulus of elasticity of rubber increases, so that if the modulus of elasticity is fixed, the amount of carbon black added can be reduced, which is advantageous in heat build-up, but the fatigue properties of rubber lower, which is apt to cause separation between carcass plies or the like and becomes disadvantageous in the durability of the tire. Therefore, the attempt for reconciling the heat build-up and fatigue properties has been unsuccessful at present.